Tea is one of the most widely consumed beverage in the world. Tea is available in many forms e.g. as green tea, black tea, hot instant tea, iced tea etc.
Green tea is generally prepared by heat treating (e.g. by steaming or pan-frying) freshly picked leaves to arrest enzyme action and then subjecting the leaves to a series of drying and rolling steps.
Black tea is generally prepared by subjecting freshly picked tea leaves to a series of processing conditions including withering and macerating the fresh tea leaves, followed by fermentation which mainly contributes to the characteristic colour, flavour and aroma of black tea. The tea is dried at high temperature after fermentation to arrest the enzyme action and to bring down the moisture to a low level.
Green tea and black tea are products which are brewed in hot water to produce tea infusions in the hot water wherefrom the tea leaf insolubles have to be filtered before the infusions are consumed. Hot instant tea is a product which contains no water insolubles. This hot instant tea product is fully soluble in hot water and this solubilized product can be consumed as such without any filtration. Iced tea is a product made from tea where the fully water-soluble fractions of tea are dissolved in water with or without additional flavours and the dissolved tea solution is kept chilled in a refrigerator before it is consumed.
The process for the preparation of hot instant tea and iced tea are described in literature. One such description can be found in the reference book ‘Tea—Cultivation to Consumption’ edited by K. C. Wilson & M. N. Clifford & published by Chapman & Hall (1992).
Many tea manufacturing processes produce by-product streams that contain aroma volatile compounds. In the leaf tea manufacture process, the dryer exhaust containing aroma volatiles can be cooled to obtain an aqueous condensate containing aroma volatile compounds. The evaporator condensate stream in instant tea manufacturing processes also contains aroma volatile compounds. However, the aroma in these condensate streams is usually present at very low levels. Typically the concentration of aroma volatiles in the condensate streams is below 500 mg/l, and often less than 50 mg/l and can be as low as 10 mg/l. This dilute nature of the aroma in the condensate streams restricts their application as a source of aroma for add-back. These condensate steams are often not utilized or are limited in their use due to the extremely low concentrations. In many cases these streams are even discarded, leading to loss of precious aroma bearing compounds. This is because the known processes for recovery of these compounds are either not technically and/or commercially viable or are very inefficient. Tea aroma is one of the most important factors for determining tea quality. Hence tea with good aroma profile fetches a premium in the market. Recovery of aroma volatile compounds from the condensate streams can provide a source of natural tea aroma that can be used for add-back and improving the aroma of the tea.
Many processes to recover and concentrate volatile compounds from dilute streams have been known and practised. These processes include reverse osmosis, distillation, cryoconcentration, freeze drying, staged/partial condensation and pressure swing adsorption. Distillation has always been one preferred process. GB 1061009 (Salada Foods, 1967) describes a process for recovery of aroma from aqueous tea streams using distillation carried out in an inert atmosphere. The present inventors have determined that using the method described in the GB publication, the quality of the tea aroma recaptured improves to a small extent but a large percentage of the aroma present in the tea aqueous extract can not be recovered using this process and there are high losses.
It is thus an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art.
It is an object of the present invention to provide for a process for the enhanced recovery of volatile compounds from aqueous tea extract streams like condensate streams from hot instant tea and ice tea manufacture.
It is another object of the present invention to provide for a process for the recovery of volatile compounds like aroma compounds in more concentrated forms as compared to known processes of the prior art.